Gamma ray detectors are used in a wide variety of apparatus, such as in positron emission tomograph (PET), single photon emission-computed tomograph (SPECT), explosive detectors, and the like. All of such apparatus depend upon, in part, detectors which can determine the position of interactions of gamma rays with the detectors, such that with a plurality of such position measurements, a scan of an object of interest can be made. These techniques are well known in the art and need not be detailed herein.
The difficulty with all such detectors is that in order to perform a scan, a multiplicity of such detectors are necessary, and the positions of interactions of gamma rays with the detectors must be determined so that with a plurality of such determinations, e.g. in the millions, sufficient data is obtained to produce an accurate scan image of the object of interest. Since each of the detectors must be capable of generating position data for a gamma ray interaction, acquisition of such position data and the compilation thereof, e.g. by a computer, requires very substantial and expensive apparatus. Typically, the data of such detectors is initiated by a generation of light in a scintillator material of the detector as the gamma ray interacts therewith. By determining the detector in which such light was emitted, and the position of that emitted light within the detector, a data point for a scan is produced. By providing a multiplicity of such detectors, which can, depending upon the application, be in the thousands of detectors, a multiplicity of data points can be acquired and, by computer compilation, resolved into an image of the object of interest being scanned.
Typically, for example, four photodetectors will be instrumented with an array of scintillating detectors where the photodetectors detect the emission of light in the scintillating detectors. A logic circuit can be employed to determine the position of emitted light. However, as can be appreciated, the monitoring instrumentation, including the photodetectors, logic circuits and related controller and signal devices (referred to collectively as a read-out channel) results in very complex monitoring instrumentation, especially when a large number of detectors are required for the intended scan.
In addition, the usual detector for such gamma ray scanning devices is an inorganic scintillating crystalline material, e.g. cerium doped lutetium oxyorthosilicate (LSO) and bismuth germinate (BGO), which is, in and of itself, expensive. The crystalline material is a scintillator material which will emit light and therefore the position of interaction of a gamma ray can be determined. The X-Y position resolution of such detectors is typically 20 square millimeters and typically is not uniform for all positions, and this leaves a basic inaccuracy in not knowing precisely where in the detector, i.e. in the X and Y coordinates, that interaction occurred. In addition, the depth of the interaction, i.e. the Z coordinate, is generally not determined, or is poorly determined, resulting in a so-called parallax error and further image inaccuracy. Those effects result in less than desirable accuracy of scan images for the object of interest.
As can be appreciated from the above, it would be of decided advantage to the art to provide a gamma ray detector which can be inexpensively constructed, requires far less monitoring instrumentation for acquisition of the required data, and which can determine the X, Y and Z coordinates of the gamma ray interaction.